An internal combustion engine converts a portion of chemical energy in a fuel into rotational energy and heat. A portion of heat energy generated by the engine may be regarded as waste heat energy. U.S. Pat. No. 7,353,661 describes a system where engine heat is extracted from engine coolant or exhaust gases to power a generator. A same refrigerant that is used to generate electricity is also used to cool a cabin of a vehicle. The electricity produced from engine heat may be stored in a battery or used within the vehicle. However, it may not always be beneficial to extract heat from the engine to produce electricity. For example, it may not be desirable to extract heat from the engine when the engine is being started from cold conditions because engine emissions and fuel economy may degrade. Consequently, the system may not be operated, or if the system is operated during cold engine conditions, it may not provide a desired output.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine system, comprising: an engine including an evaporator position along an exhaust system; an expander in fluidic communication with the evaporator; a condenser in fluidic communication with the evaporator; an engine coolant heat exchanger in thermal communication with the condenser, the engine coolant heat exchanger including an output that is in fluidic communication with an input of the evaporator.
By extracting engine exhaust gas heat, it may be possible to both generate electricity and improve engine warm-up so as to improve engine fuel economy and emissions. In particular, heat extracted from engine exhaust may be routed to an expander and/or to an engine heat exchanger where engine exhaust heat may be transferred to engine coolant to heat the engine. The warmed engine coolant may allow the engine to reach a desired engine operating temperature in a shortened period of time, thereby reducing engine emissions and improving fuel economy. In one example, a bypass valve may be selectively operated to route a heat transfer medium or working fluid to either or both of an expander and an engine coolant heat exchanger. In this way, it may be possible to improve the functionality of an exhaust gas heat recovery system.
The present description may provide several advantages. In particular, the approach may improve engine starting emissions and fuel economy by reducing engine warm-up time. Further, the approach may extract engine heat from several locations so that less engine exhaust gas heat may be necessary to operate an expander that rotates a generator. Further still, the approach may provide heat to a vehicle cabin sooner than systems that rely solely on heat from an engine block to provide cabin heat.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.